*{
    padding:0;
    margin: 0;
    box-sizing: border-box;
}
.built-in-app{
    width: 700px;
    margin: auto;
}
.built-in-app li{
    list-style: none;
    position: relative;
    display: inline-block;
    padding: 5px;
    margin: 0 14px;
    cursor: pointer;
}
.built-in-app .nav .active{
    color: indigo;
    font-weight: bolder;
}
.built-in-app .nav > .active:after{
    border-bottom: 5px solid orangered;
    content: "";
    position: absolute;
    width: 100%;
    left: 0;
    bottom: -1px;
}
.built-in-app .main > div{
    display: none;
}
.built-in-app .main>.active{
    display: block;
}

.aa{
    padding-top: 25px;
    width: 320px;
}
.aa span{
    color: orange;
    font-size: 18px;
    font-weight: 100;
}
.aa .foal li{
    padding: 10px 0;
    float: left;
    width: 130px;
    font-size: 10px;
}
.aa a:hover{
    color: rosybrown;
}
.aa a{
    font-size: 14px;
    text-decoration: none;
    color: #999;
}